A mechanical filter can be used to remove, filter, or collect particles. This filtering and collection of particles can be used for sampling of particles, chemical detection, and/or biological cell analysis.
It is known to make such filters using micromachining techniques to form small features in a silicon wafer. For example, this has been described in C. J. M. Van Rijin and M. C. Elwenspoek, xe2x80x9cMicro Filtration Membrane Sieve with Silicon Micro Machining for Industrial and Biomedical Applications,xe2x80x9d Proceedings of IEEE Micro Electro Mechanical Systems Workshop (MEMS""95), pp. 83-87, 1995 and G. Kittilsland and G. Stemme, xe2x80x9cA Submicron Particle Filter in Silicon,xe2x80x9d Sensors and Actuators, A: Physical, Vol. 23, pp. 904-907, 1990. However, the present disclosure describes a different way of developing filters which has certain improved characteristics. One problem with prior micromachined filters is their overall strength.
A membrane particle filter is described which uses micromachining technologies. The filters are fabricated using a substrate membrane that is perforated with holes. The holes can have different shapes, different dimensions, and different opening factors. Preferred shapes include circular, hexagonal, and rectangular, with dimensions ranging from 6-13 xcexcm.
In a preferred mode, a layer of Parylene material is uniformly coated on the filters and on the inner surfaces of the holes in order to increase the overall strength of the filter.
Another important feature is the amount of power which is necessary to provide the desired pressure drop across the filter. Proper control of the opening size allows determining various tradeoffs, including the energy and power necessary to form the desired pressure drop. Another feature of this disclosure is that the sizes of the openings can be more specifically controlled by deposition of Parylene material.